Not Applicable
Not Applicable
The present invention relates to a controller for an array of miniature therapeutic radiation sources.
In the field of medicine, radiation may be used for diagnostic, therapeutic and palliative purposes. Therapeutic use of radiation such as x-rays and xcex3-rays typically involves using these rays to eradicate malignant cells. Conventional radiation treatment systems used for medical treatment, such as linear accelerators that produce high-energy x-rays, utilize a remote radiation source external to the targeted tissue. A beam of radiation is directed at the target area, for example a malignant tumor inside the body of a patient. The x-rays penetrate the patient""s body tissue and deliver radiation to the cancer cells, usually seated deep inside the body. This type of treatment is referred to as teletherapy because the radiation source is located at some distance from the target. This treatment suffers from the disadvantage that tissue disposed between the radiation source and the target is exposed to radiation. To reach the cancer cells, the x-rays from an external radiation source must usually penetrate through normal surrounding tissues. Non-cancerous tissues and organs are thus also damaged by the penetrating x-ray radiation.
Brachytherapy, on the other hand, is a form of treatment in which the source of radiation is located close to, or in some cases within, the area receiving treatment. Brachytherapy, a word derived from the ancient Greek word for close (xe2x80x9cbrachyxe2x80x9d), offers a significant advantage over teletherapy, because the radiation is applied primarily to treat only a predefined tissue volume, without significantly affecting the tissue adjacent to the treated volume. The term brachytherapy is commonly used to describe the use of xe2x80x9cseeds,xe2x80x9d i.e. encapsulated radioactive isotopes, which can be placed directly within or adjacent to the target tissue that is being treated. Handling and disposal of such radioisotopes, however, may impose considerable hazards to both the handling personnel and the environment. Also, introduction of the radioisotopes requires invasive procedures which have potential side-effects, such as the possibility of infection. Moreover, there is no ability to provide selective control of time dosage or radiation intensity.
The term xe2x80x9cx-ray brachytherapyxe2x80x9d is defined for purposes of this application as x-ray radiation treatment in which the x-ray source is located close to or within the area receiving treatment. An x-ray brachytherapy system, which utilizes a miniaturized low power radiation source that can be inserted into, and activated from within, a patient""s body, is disclosed in U.S. Pat. No. 5,153,900 issued to Nomikos et al., U.S. Pat. No. 5,369,679 to Sliski et al., U.S. Pat. No. 5,422,926 to Smith et al., and U.S. Pat. No. 5,428,658 to Oettinger et al., all owned by the assignee of the present application, all of which are hereby incorporated by reference.
The x-ray brachytherapy system disclosed in the above-referenced patents includes a miniaturized, insertable probe capable of producing low power x-ray radiation while positioned within or in proximity to a predetermined region to be irradiated. In this way, x-ray radiation need not pass through the patient""s skin, bone, or other tissue prior to reaching the target tissue. The probe may be fully or partially implanted into, or surface-mounted onto a desired area within a treatment region of a patient. X-rays are emitted from a nominal, or effective xe2x80x9cpointxe2x80x9d source located within or adjacent to the desired region to be irradiated, so that substantially only the desired region is irradiated, while irradiation of other regions are minimized. X-ray brachytherapy offers the advantages of brachytherapy, while avoiding the use and handling of radioisotopes. Also, x-ray brachytherapy allows the operator to control over time the dosage of the delivered x-ray radiation.
X-ray brachytherapy treatment generally involves positioning the insertable probe into or adjacent to the tumor or the site where the tumor or a portion of the tumor was removed to treat the tissue adjacent the site with a local boost of radiation. X-ray probes of the type generally disclosed in U.S. Pat. No. 5,153,900 include a capsule, and a hollow, tubular probe or catheter extending from the capsule along an axis, and having an x-ray emitting target element at its distal end. The probe may enclose an electron source, such as a thermionic cathode. In one form of a thermionic cathode, a filament is resistively heated with a current. This in turn heats the cathode so that electrons are generated by thermionic emission.
In another form of an x-ray brachytherapy device, as disclosed in U.S. Pat. No. 5,428,658, an x-ray probe may include a flexible probe, such as a flexible fiber optic cable enclosed within a metallic sheath. The x-ray probe may also include a substantially rigid, evacuated capsule that is coupled to a distal end of the flexible probe. The capsule encloses an optically activated electron source, such as a photocathode, and an x-ray emissive target element. In a photocathode configuration, a photoemissive substance is irradiated by a LED or a laser source, causing the generation of free electrons. Typically, a flexible fiber optic cable couples light from a laser source or a LED to the photocathode.
U.S. Pat. No. 6,480,568 entitled xe2x80x9cOptically Driven Therapeutic Radiation Source,xe2x80x9d issued on Nov. 12, 2002 to Mark Dinsmore, and hereby incorporated by reference in its entirety)(hereinafter the xe2x80x9c""568 patentxe2x80x9d) discloses an optically driven (for example, laser driven) therapeutic radiation source using a reduced-power, increased efficiency electron source, which generates electrons with minimal heat loss. The ""568 patent discloses the use of laser energy to heat an electron emissive surface of a thermionic emitter, instead of using an electric current to ohmically heat an electron emissive surface of a thermionic emitter. With the optically driven thermionic emitter, electrons can be produced in a quantity sufficient to produce the electron current necessary for generating therapeutic radiation at the target, while significantly reducing the requisite power requirements. U.S. patent application Ser. No. 10/005,290 and hereby incorporated by reference)(hereinafter the xe2x80x9c290xe2x80x9d application) discloses a therapeutic radiation source having an in situ radiation detector, which permits real-time monitoring of the therapeutic radiation that has been generated and delivered.
Even though the above-discussed miniature radiation sources can generate x-rays local to the target tissue, it is difficult to provide a uniform, or other desired, dose of radiation to an irregularly shaped target tissue, using these radiation sources. These miniature radiation sources generally act as point sources of therapeutic radiation. The intensity of the radiation from a point source decreases uniformly with approximately the square of the distance (R) from the source (i.e., 1/R2). Since body cavities, or the beds of resected tumors, are not generally spherically symmetrical, a point source within a body cavity or central to the resected tumor bed will not deliver a uniform dose of radiation to the tissue lining of the cavity or bed. Likewise, a point source at the center of a non-spherical tumor will not deliver radiation with an isodose contour matching the peripheral surface of the tumor.
The organs or body cavities being treated during radiation therapy usually have arbitrary and irregular shapes and geometries. The areas of a patient""s body requiring treatment may be characterized by twists and bends. In some cases, the geometry of the target region may not be fixed, as in the bladder for example, which has a flexible inner wall without a well-defined shape. Also, some treatment procedures may require delivery of localized radiation to portions of the human body that are not easily accessible. Cancerous tumors are usually shaped irregularly, and are distributed randomly across a given anatomical region.
A single point source of therapeutic radiation, even when inserted into and activated within a patient""s body, cannot deliver a uniform dose of radiation to a desired area within an irregularly shaped body cavity or organ, nor can it deliver more complex radiation dose patterns that may be desirable or required for some cases. Similarly, a single point source at the center of a non-spherical tumor will not deliver radiation with an isodose contour matching the peripheral surface of the tumor, as discussed earlier.
U.S. Pat. No. 6,556,651 (entitled xe2x80x9cArray of Miniature Radiation Sources,xe2x80x9d issued on Apr. 29, 2003 to Euan Thomson and Mark Dinsmore, and hereby incorporated by reference in its entirety)(hereinafter the ""651 patent), discloses a system for delivering therapeutic radiation that includes a plurality of point-like sources that are arranged over the desired treatment region as a one- or multi-dimensional array. A plurality of point radiation sources permits a more effective and versatile delivery of radiation over irregularly shaped treatment regions, as compared to a single point source of therapeutic radiation.
In order for a surgeon or other radiotherapy to use such an array of sources to build up complex, multi-dimensional dose patterns that he believes appropriate for the conditions of his patient, a controller is needed that can manipulate and selectively drive the array. There is a need for a controller that can control the intensity and duration of the therapeutic radiation emitted from each individual therapeutic radiation source in the array. The physician or other operator of the array of sources must be able to independently vary, for each therapeutic radiation source, parameters such as the turn-on time of the laser source, turn-on time of the high voltage source, the magnitude of the accelerating voltage provided to the electrons, and the magnitude of the electron beam current formed by the accelerated electrons.
The present invention is directed to a controller for an array of therapeutic radiation sources, for example x-ray sources. Each therapeutic radiation source includes an electron source and an associated target element. The controller allows each therapeutic radiation source to be selectively operated, so as to generate therapeutic radiation at selected time intervals and at selected intensities. The controller includes intensity control circuitry for independently controlling the intensity of the therapeutic radiation generated by each therapeutic radiation source. The controller also includes duration control circuitry for independently controlling the duration of the therapeutic radiation generated by each radiation source. The controller may also include means for controlling the position of each radiation source within the treatment region, for example a mechanical introducer for inserting the therapeutic radiation sources into a treatment region and withdrawing the radiation sources from the treatment region.
In one embodiment, each therapeutic radiation source is coupled to an associated fiber optical cable, so that the array of therapeutic radiation sources includes a plurality of fiber optical cables and a corresponding plurality of therapeutic radiation sources. Alternatively, a single fiber optical cable can be used, having one originating end and a plurality of terminating ends. Light is generated by an optical source and transmitted through a fiber optical cable, and impinges upon the electron source, causing emission of electrons. An accelerating voltage is provided between each electron source and each associated target element. The target element emits therapeutic radiation in response to incident accelerated electrons from the electron source. The generated electrons may form an electron beam along a beam path.
The intensity control circuitry may include programmable means for user-controlled adjustment of the amplitude of the accelerating voltage, or the magnitude of the current formed by the electron beam. The duration control circuitry may include means for selectively activating a high voltage power supply that provides the accelerating voltage between each electron source and its associated target element. The duration control circuitry may also include means for selectively activating the optical source.
The mechanical assembly may be an introducer for controllably effecting a reversible displacement of a linear or planar array of therapeutic radiation sources, into and out of a desired treatment region. Alternatively, the mechanical assembly may be an introducer that allows independent movement of each therapeutic radiation source with respect to each other.
The controller may regulate an in situ radiation detecting system that may be provided for monitoring in real time an amount of the therapeutic radiation emitted by each therapeutic radiation source. The controller may also regulate an image-guided surgery system that can generate in real time a visual image representing a cumulative dose of radiation delivered by each therapeutic radiation source to desired locations within the treatment region.
The present invention features a method for treating an anatomical region in a patient. The method includes positioning an array of x-ray sources near the anatomical region. For example, the array of x-ray sources may be inserted into a body passageway, such as a blood vessel, and the array may be guided through the body passageway so that each x-ray source is positioned at a desired location with respect to the anatomical region. The method includes selectively activating one or more of the x-ray sources in the array, so as to irradiate the anatomical region according to a desired and predetermined irradiation profile.